The present invention relates to a pneumatic tire more particularly to a radial tire having an improved belt structure being capable of reducing the tire weight.
Multi-filament cords made of a plurality of steel filaments twisted together are widely used in the belts of belted radial tires.
In recent years, in order to reduce the tire weight and cost, a belt composed of monofilament steel cords has been proposed.
However, in comparison with multi-filament cords, the monofilament cords are high in the bending rigidity and inferior in the fatigue resistance and durability. As a result tire performance such as ride comfort, steering stability during cornering and the like is not good.
It is therefore, an object of the present invention to provide a radial tire improved in the durability, ride comfort, steering stability and the like, while achieving weight reduction and cost reduction.
According to one aspect of the present invention a pneumatic tire comprises a carcass extending between bead portions through a tread portion and sidewall portions, and a belt disposed radially outside the carcass in the tread portion, the belt comprising a monofilament cord ply made of waved monofilament cords and a multi-filament cord ply made of multi-filament cords. Preferably, each waved monofilament steel cord has a cross sectional area of from 0.09 to 0.30 sq.mm. The waved monofilament steel cord is (1) spirally waved so that the wave pitches PA are in a range of from 14 to 50 mm and the amplitude HA of each wave is in a range of from 0.002 to 0.02 times the pitch PA of the wave, or (2) two-dimensionally waved so that the wave pitches PB are in a range of from 5 to 50 mm, and the amplitude HB of each wave is in a range of from 0.002 to 0.05 times the pitch PB of the wave.
According to another aspect of the present invention a pneumatic tire comprises a carcass extending between bead portions through a tread portion and sidewall portions, and a belt disposed radially outside the carcass in the tread portion, the belt comprising two monofilament cord plies made of waved monofilament cords. Preferably, the waved monofilament steel cord is waved so that the wave pitches P are in a range of from 0.008 to 0.08 times the circumference of the tire and the wave height of each wave is in a range of from 0.002 to 0.025 times the pitch P of the wave. The waved monofilament steel cord has an average thickness of from 0.13xc3x9710xe2x88x923 to 0.28xc3x9710xe2x88x923 times the circumference of the tire.